With the rapid development of electronic technologies, the power rating of power supply equipment continuously increases, and the standard of harmonic currents gets universal and lowered. Nowadays, power factor correction (PFC) converters are increasingly used in power supply designs to improve power factors of electric equipment. The conventional bridge PFC converter is widely used in the front end of AC/DC power stage due to its simple circuit structure and low common-mode noise. However, the energy transfer path will cause high conduction and switching loss as more semiconductor devices are used due to the presence of a rectifying bridge.
In order to reduce the loss of switches in the PFC circuit, a bridgeless PFC has been applied. For application of the bridgeless PFC, the critical problems include phase detection of alternating voltage and zero current detection when the PFC inductor current is in a critical discontinuous mode (DCMB for short).
In prior art, an AC voltage of the input PFC circuit is obtained by detecting the inductor voltage at the input of the PFC circuit, and a zero-crossing detection signal of this voltage is extracted and sent to a DSP/MCU, which processes the signal in a digital way through sequentially-executed operations such as determination of the phase of the input voltage, selection of the zero-crossing detection (ZCD for short) signal, frequency limiting operation on the zero-crossing detection signal, and the like to generate the control signals of the switches in the PFC circuit.
In the prior art, the operations such as processing of the ZCD signal by the DSP/MCU and frequency limiting operation require high performance of the DSP/MCU, especially when used in high-frequency applications since a significant signal delay will be introduced by DSP/MCU while processing high-frequency ZCD signals, if worse, the accuracy of signal processing in the entire system where the PFC is located will be affected.